Preparation of activated carbon from Camellia oleifera shell and its application to adsorption of hexavalent chromium from aqueous solution: kinetics, equilibrium, and thermodynamics

Preparation of the adsorbent was performed by pyrolysis carbonization and followed by potassium hydroxide (KOH) activation of Camellia oleifera shell under the nitrogen atmosphere. Through the thermogravimetric–derivative thermogravimetric analysis, the range of carbonization temperature was set from 300°C to 400°C increased 50°C at a time. The optimum carbonization and activation conditions were investigated by the orthogonal experiment. The activated carbon was characterized by scanning electron microscopy, Brunauer–Emmett–Teller, and Fourier transform infrared spectroscopy. The adsorption of hexavalent chromium (Cr(VI)) from aqueous solution by C. oleifera shell activated carbon was carried out with batch adsorption experiments. The effects of initial pH value, adsorbent dosage, the temperature on the adsorption were studied. The results indicate that the activated carbon is an effective adsorbent with a high surface area (1,585.60 m2/g) and a large pore volume (1.055 cm3/g). The adsorption process follows the pseudo-second-order kinetic model. The adsorption equilibrium data obtained at 25°C, 35°C, and 45°C fit better with the Freundlich model than Langmuir model and the thermodynamics parameters, ΔH°, ΔS°, and ΔG° were calculated. It indicates that the process of Cr(VI) adsorption on activated carbon is entropy-driven and endothermic. The results illuminate that C. oleifera shell activated carbon is an effective adsorbent for adsorbing Cr(VI) from aqueous solutions.